The official, speaking to AFP on condition of anonymity, said there were indications the Iraqis had tried to create an international incident by altering the route of the convoy to pass through a contested area west of Baghdad on Sunday.
"It looks like it was a trap set by the Iraqis," the official said.
The State Department said the Russians had given US diplomats precise details of the description and number of vehicles in the convoy, the people in them as well as the exact route they would take out of the Iraqi capital.
This information was passed to US military commanders to prevent the convoy from facing fire from coalition forces who have surrounded Baghdad, deputy spokesman Philip Reeker said.
"We were in contact with Russian authorities over the past several days, before this incident, to discuss the withdrawal of their personnel from Baghdad," Reeker told reporters.
"We provided our military with detailed information about the vehicles and the personnel involved, as well as the route that they planned to follow," he said.
Reeker declined to comment on whether the route was changed, saying the matter was under investiagtion, but the US official said it appeared the convoy had not followed its planned path out of Baghdad.
"It seems the Iraqis may have told them to take a different route than they told us because we didn't have anyone in the area they were supposed to be in," the official added.
The official said last-minute changes to the route might explain why US Central Command at first maintained there were no coalition troops in the area where the convoy was traveling when it was hit.
The convoy carrying Russian ambassador to Iraq, Vladimir Titorenko, and other embassy staff came under fire shortly after it left Baghdad, injuring the envoy and at least four others.
According to witness accounts, the convoy was caught in crossfire between US and Iraqi soldiers although the reports were not clear as to which side shot first.
The US official said the first reports from the US military indicated that the Iraqis had fired first but stressed the investigation into the incident was still in its preliminary stages.
"From what we can tell, We had guys coming into the area, the convoy coming into the area and the Iraqis were waiting," the official said. "When the vehicles came by, the Iraqis started shooting."
The official said there had been no intention to attack the Russian ambassador. "That's why we think the Russians followed a different route."
The attack has, however, further strained tense ties between Washington and Moscow and US Secretary of State Colin Powell (news - web sites) called his Russian counterpart Igor Ivanov on Sunday to assure him a full investigation into the matter was underway.
In Moscow, visiting US national security advisor Condoleezza Rice (news - web sites) told Russian President Vladimir Putin (news - web sites) that if US troops had fired on the convoy during a crossfire they had meant no harm to the diplomats.
